Investigators

Period of Record

1972-2007

Methods

At Christmas Island, weekly air samples are collected in 5-L evacuated glass flasks exposed in triplicate. Flasks are returned to the SIO for CO2 determinations, which are made using an Applied Physics Corporation nondispersive infrared gas analyzer. The 1972-1976 portion of this record is based on air samples collected at Fanning Island. The 1977-1983 portion of this record is based on air samples collected at both Christmas Island and Fanning Island. From 1983 to present the record is based solely on air samples collected at Christmas Island. In May 1983, the CO2-in-N2 calibration gases were replaced with CO2-in-air calibration gases, which are currently used (Keeling et al. 2002). Data are in terms of the Scripps "03A" calibration scale.

Trends

On the basis of flask samples collected at Christmas Island and analyzed by SIO, the annual
average of the fitted concentrations of CO2 rose from 332.04 ppmv in 1975 to 383.61 ppmv in 2007. This represents an average annual growth rate of over 1.61 ppmv per year in the fitted values at Christmas Island.

References

Bacastow, R.B. 1979. Dip in the atmospheric CO2 level during the mid-1960's. Journal of Geophysical Research 80:3109-14.